The subject of the present invention is an actuating device for a master cylinder, especially intended to equip a braking circuit of a motor vehicle.
It is known that such master cylinders comprise at least one piston whose actuation induces an increase in the pressure of a hydraulic fluid in at least one working chamber, this increase in pressure being transmitted by pipes to brake motors in order to immobilize the wheels of the vehicle so equipped. The actuation of the piston of the master cylinder takes place, in a known manner, either by a rod directly attached to the brake pedal, or by the pushrod of a pneumatic brake booster which can itself be actuated by the brake pedal.
It may happen that, in certain situations, although numerous precautions are taken, the actuating rod of the master cylinder piston loses contact with the latter. These cases may for example occur when various springs providing a return to the rest position are fatigued, when the manufacturing tolerances accumulate and introduce large play, or when vibrations occur in the braking circuit. The latter possibility may, for example, originate from the interposition in the braking circuit of an anti-lock device for the wheels which, during its periods of operation, modulates the pressure in the braking circuit at a high rate. Thus, vibrations occur at the interface between the piston of the master cylinder and the actuating rod, which vibrations generate noise and are capable of inducing rotation of the actuating rod, the loss of adjustments carried out on this and premature wear of the components.
The subject of the invention is, therefore, an actuating device for a master cylinder for the braking circuit of a motor vehicle, which provides the centering of the actuating rod with respect to the piston of the master cylinder, which prevents their relative rotation, which avoids vibrations and noise between these two components, and which limits their wear.
Document US-A-3 010 772 discloses the use of a resilient retainer means forbidding an axial relative movement of the rod with respect of the piston of the master cylinder. However this retainer means does not act for radially maintaining the rod with respect of the piston.